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Introduction: Why Molecular Glues Are the Hottest Trend in Oncology

For years, precision oncology has revolved around kinase inhibitors and monoclonal antibodies. Yet nearly 80% of cancer-relevant proteins remain “undruggable” because they lack the deep pockets that classic small molecules need. A new wave of molecular glue degraders is rewriting that rulebook by using the cell’s own ubiquitin–proteasome system to destroy oncogenic proteins instead of merely blocking them.

These next-generation small molecules are emerging as a powerful strategy to target transcription factors, scaffold proteins, and other elusive drivers of malignancy. As AI-guided design and chemoproteomics converge, molecular glues are poised to become a central pillar of future cancer therapy.

What Exactly Are Molecular Glue Degraders?

Molecular glues are monovalent small molecules that stabilize a normally weak or non-existent interaction between a disease-causing protein and an E3 ubiquitin ligase. This induced proximity leads to ubiquitination and subsequent proteasomal degradation of the target protein.

Unlike traditional inhibitors, which typically block an active site, molecular glues act more like “chemical matchmakers”:

• They bind to an E3 ligase (or sometimes the target) and remodel its surface.
• They create a new protein–protein interface that recruits a specific target protein.
• The target is polyubiquitinated and sent to the proteasome for degradation.

A landmark example is lenalidomide, which binds to the E3 ligase cereblon and promotes degradation of the transcription factors IKZF1 and IKZF3, explaining its potent anti-myeloma activity (doi:10.1038/nature13526).

Why Molecular Glues Are Game-Changers for “Undruggable” Cancer Targets

Molecular glues unlock drug discovery space that was previously inaccessible:

• Directly degrading transcription factors: Oncogenic factors like MYC or BCL6 lack enzymatic pockets but are central to tumor survival. Degrading them can dismantle entire oncogenic programs rather than nudging one pathway node.
• Catalytic pharmacology: One glue molecule can trigger the degradation of many target molecules, potentially allowing lower doses and improving safety.
• Bypassing resistance: Tumors that acquire mutations in inhibitor binding sites may still be vulnerable to degradation strategies that exploit different, often distal, protein surfaces.

For instance, the cereblon modulator CC‑90009 acts as a molecular glue that recruits the translation termination factor GSPT1 to cereblon, promoting its degradation and showing strong activity in acute myeloid leukemia models (doi:10.1158/2159-8290.CD-19-0182).

Molecular Glues vs. PROTACs: Same Destination, Different Road

Both molecular glues and PROTACs (PROteolysis TArgeting Chimeras) aim to remove disease-driving proteins, but their design principles differ:

• PROTACs: Large, heterobifunctional molecules with two distinct ligands (one for the target, one for the E3 ligase) connected by a linker.
• Molecular glues: Compact, single-pharmacophore molecules that remodel an existing ligase surface to capture a new substrate.

Because of their smaller size, molecular glues often have more favorable oral bioavailability, cell permeability, and pharmacokinetics. Structural studies show that subtle chemical tweaks can flip a “simple binder” into a glue that creates a new protein–protein interface (doi:10.1038/s41573-021-00210-7).

Emerging Targets and the AI-Driven Glue Discovery Pipeline

The field is rapidly expanding beyond immunomodulatory drugs:

• Oncogenic transcription factors: Rational design and phenotypic screens are uncovering glues that redirect E3 ligases toward factors like BCL6 and potentially MYC.
• Scaffold and adapter proteins: Components of signaling complexes, once considered undruggable, can now be selectively depleted to collapse entire oncogenic networks.
• Cancer-specific neo-substrates: Molecular glues can exploit mutations or altered expression in tumors to create substrates that do not exist in normal cells, increasing therapeutic window.

AI and chemoproteomics are central to this revolution. Systematic mapping of ligandable hotspots and ligase interactomes is enabling the de novo discovery of glue chemotypes with high selectivity and potent degradation profiles (doi:10.1038/s41573-022-00506-0).

Key Challenges and What Comes Next

Despite their promise, molecular glues face important hurdles:

• Target prediction: Not every protein can be turned into a degradable neo-substrate. We still lack robust rules to predict “glue-ability.”
• Safety and durability: Chronic depletion of essential proteins may cause delayed toxicities that differ from classic inhibitors.
• On-target, off-tumor effects: When the target is also crucial in normal tissues, fine-tuning dose, schedule, and ligase choice becomes critical.

As machine learning, structural biology, and high-throughput chemoproteomics converge, the next decade is likely to bring a wave of first-in-class molecular glue cancer drugs that finally crack some of oncology’s most intractable targets.

References

• Lu, G. et al. The myeloma drug lenalidomide promotes the cereblon-dependent destruction of Ikaros proteins. Nature 511, 621–626 (2014). doi:10.1038/nature13526
• Hattori, T. et al. CC‑90009, a cereblon E3 ligase modulator, targets GSPT1 for degradation and exhibits potent antileukemic activity. Cancer Discov. 10, 1754–1771 (2020). doi:10.1158/2159-8290.CD-19-0182
• Pettersson, M. & Crews, C. M. Proteolysis targeting chimeras (PROTACs)—Past, present and future. Nat. Rev. Drug Discov. 18, 421–446 (2019). doi:10.1038/s41573-021-00210-7
• Mayor‑Ruiz, C. & Winter, G. E. Systematic identification of molecular glue degraders by chemoproteomics. Nat. Rev. Drug Discov. 22, 141–160 (2023). doi:10.1038/s41573-022-00506-0